10 In what sense, then, did our Lord say here, “I have power to lay down my soul [life]”? Who lays down his soul, and takes it again? Is it as being the Word that Christ does so? Or is it the human soul He possesses that lays down and resumes its own existence? Or is it His fleshly nature that lays down its life and takes it again? Let us sift each of the three questions I have suggested, and choose that which conforms to the standard of truth. For if we say that the Word of God laid down His soul, and took it again, we should have to fear the entrance of a wicked thought, and have it said to us: Then there was a time when that soul was separated from the Word, and a time, after His assumption of that soul, when He was without a soul.
I see, indeed, that the Word was once without a human soul, but only so, when “in the beginning was the Word, and the Word was with God, and the Word was God.” But from the time that the Word was made flesh, to dwell among us, and manhood was assumed by the Word, that is, our whole nature, soul and flesh, what more could His passion and death do than separate the body from the soul? It separated not the soul from the Word. For if the Lord died, yea, because He died (for He did so for us on the cross), doubtless His flesh breathed out that which was its life: for a short time the soul forsook the flesh, although destined by its own return to raise the flesh again to life.
But I cannot say that the soul was separated from the Word. He said to the soul of the thief, “Today shall you be with me in paradise.” He forsook not the believing soul of the robber, and did He abandon His own? Surely not; but when the Lord took that of the other into His keeping, He certainly retained His own in indissoluble union. If, on the other hand, we say that the soul laid down and reassumed itself, we fall into the greatest absurdity; for what was not separated from the Word, was inseparable from itself.
Source: Tractates on the Gospel of John (New Advent)